The invention relates to locking device for bicycles, comprising a nut which can be screwed onto a threaded rod of the bicycle, a key part and a cap, the base of which, when the nut is located on its thread, is situated between the nut and a part of the bicycle which is opposite the nut, and the cylindrical wall of which cap surrounds the nut and ends in the region of the end face of the nut, and which cap, in the tightened state, is freely rotatable, the surfaces of the nuts of a plurality of bicycles differing from one another and that part of the key part of a bicycle which engages the nuts being adapted in a positively locking manner to certain nuts of this bicycle.
In a known locking device of this kind (U.S. Pat. No. 4,674,306), the key part is rigidly connected to a lock for locking the bicycle, for example to a fixed post. The differences in respect of the nut surfaces are limited to the end faces of the nut. The cap is positioned in a sliding manner, i.e. practically without clearance, on the nut (with a circular peripheral face).
This locking device has a number of drawbacks: the combination of key and lock is disadvantageous in as much as anyone who breaks open the lock then has the key at his disposal and can thus loosen the nut. Under certain circumstances it may even be that the key protection is unimportant for anyone who breaks open the lock, which can be carried out without a problem using an appropriate tool, since he is then able to steal the entire bicycle. The fact that the differences with respect to the nut surfaces are limited to the end faces of the nuts has the disadvantage that a thief can loosen a nut using hammer and chisel. He is also able to loosen the nuts if he compresses the cap using a strong pair of pliers and thus presses against the nut and then turns the cap and nut using the pair of pliers.
The object of the invention is to design the locking device mentioned at the outset such that greater security compared to the known case is provided with regard to loosening the nuts or theft of individual parts of the bicycle, in particular the wheels and/or the saddle.